Work holder



y'zs, 1957 o. E. STAPLES 2,793,865

' WORK HOLDER Filed Jtly 17, 1953 5 She'ets-Sheet 1 y 8, 1957 o. E. STAPLES 2,793,865

WORK HOLDER Filed July 1?, 1955 5 Shets-Sheer, 2

INVENTOR. 07/6 E. SMPLES A TTOR/VE v5 May 28, 1957 o. E. STAPLES 2,793,865

WORK HOLDER Filed July 17, 1953 5 Sheets-Sheet Z INVENTOR. 0775 674F455 ATTORNEYS May 28, 1957 o. E. STAPLES 2,793,865

WORK HOLDER Filed July 17, 1953 5 Sheets-Sheet 4 sz I 85 IN V EN TOR.

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A TTO/E/VE K5 y 28, 1957 v o. E. STAPLES 2,793,865

WORK HOLDER Filed July 17, 1953 v v 5 Sheets-Sheet 5 JNVEN TOR. 07/5 5. STAPLES BY @QM W 4 uzz/V516 United States Patent WORK HOLDER Otis E. Staples, Euclid, Ohio, assignor, by mesne assignments, to The Farmer Manufacturing Company, a corporation of Ohio Application July 17, 1953, Serial No. 368,802

18 Claims. (Cl. 279--2) The present invention relates to hobbing machines for simultaneously hobbing a plurality of gear blanks and, more particularly, to the means for centering and securing the blanks in position to be hobbed.

The principal object of the present invention is the provision of a new and improved hobbing machine having a novel means for quickly centering and securing a plurality of annular gear blanks in position to be hobbed.

A further object of the present invention is the provision of a new and improved h-obbing machine having novel means for supporting a plurality of annular gear blanks in position to be hobbed, which means is so constructed and arranged that the blanks are individually centered about the axis of rotation of the work spindle and securely held in the centered position during the hobbing operation.

Another object of the present invention is the provision of a new and improved hobbing machine having a rotatable work spindle which includes a drive means for operating an expansible work arbor adapted to be supported thereon and rotated thereby.

Yet another object of the present invention is the provision of a new and improved expansible work arbor for individually centering each of a plurality of gear blanks about its axis, which arbor is so constructed and arranged that remaining blanks may be correctly positioned after the centering of one or more blanks.

With these and other objects in view as may hereinafter appear, the several features of the invention consist in the construction, combination and arrangements of parts hereinafter described and claimed which, with the advantages to be gained thereby, will be readily understood by one skilled in the art from the following description taken in connection with the accompanying drawing in which,

Fig. 1 is a perspective view of a bobbing machine embodying my invention;

Fig. 2 is a fragmentary view of a portion of the hobbing machine of Fig. 1 showing the work support and tailstock assembly;

Fig. 3 is a fragmentary view of the machine of Fig. 1 showing the air motor for expanding the workholder into engagement with the gear blanks positioned thereon;

Fig. 4 is a vertical sectional view taken through the workholder of the machine of Fig. 1 approximately along line 4-4 of Fig. 5; and

Fig. 5 is a sectional view taken approximately along line 5--5 of Fig. 4.

The present invention is suitable for use in machines where it is desired to position annular blanks or rings about the axis of a work support or arbor and is particularly suitable for use in hobbing machines. For purposes of illustration, the invention has been embodied in a bobbing machine of the type illustrated and described in U. S. Patent No. 2,537,967 to T. F. Carlin, issued January 16, 1951, and the patents referred to therein, the construction and operation of which will not be described in detail except where necessary for an under- 'ice standing of the construction and operation of the present invention. Sutfice it to say that the machine is of vertical construction and comprises a ,base A, a vertical column or gooseneck B supported upon the base A, a work head C vertically movable upon spaced pairs of ways 10, 11 on the column B, and a tool or hob head D carried by a cylindrical member slidably supported in a horizontal cylindrical aperture in the column B and adjustable therein towards and from the work head. The work W, in this case a plurality of gear blanks, is adapted to be rotatably supported in the work head C by an expansible arbor E attached to the upper end of a work spindle 12. A tail slide 13 is supported for vertical movement towards and from the work spindle upon ways 14, 15 formed on the work head. An air cylinder F is located in the core hole 16, is supported from the top of column B and operates a tail center member 17 slidably mounted in the tail slide. A hob spindle 18 is rotatably supported in the hob head D and during operation of the machine is rotated in timed relation to the rotation of the work spindle 12 by a cut motor located in the lower part of the column B and operatively connected to the respective spindles in a manner similar to that disclosed in the aforesaid patent.

The work head C is adapted to be vertically reciprocated along the spaced pairs of ways 10, 11 to cause the work W carried by the arbor E to be moved axially past a hob 19 fixed to the hob spindle 18 and to return the work head to its initial position by a cooperating lead screw 20 and not connected to the work head C and the base A, respectively. The lead screw is located within a chip guard 21 and is driven at a relatively slow speed in timed relation to the rotation of the hob and work spindles from the work spindle drive. The nut is rotatably supported in a housing 22 bolted to the base A and is adapted to be rotated at a relatively high speed through the medium of a self-locking worm and worm wheel drive by a high speed, reversible traverse motor located within the column B and connected to the worm by the. shaft 23.

The work spindle 12 is hollow, for reasons that will hereinafter appear, and the lower end thereof is provided with a reduced portion 24. The top of the spindle 12 is flanged and is supported by a roller bearing 25 mounted in the top of the work head housing. The reduced lower portion 24 of the work spindle is rotatably supported in a roller bearing 26 mounted in a cylindrical flange 27 extending inwardly from the bottom of the housing of work head C. The spindle 12 is rotated in timed relation to the hob through spindle drive change gears located in the gear box G on the right hand side of the work head C, which change gears mesh with a worm wheel 28 on the spindle. Feed change gears are also located within the gear box G and mesh with a worm wheel 29 fixed to the upper end of lead screw 20, as is described in detail in the aforesaid patent.

According to the present invention, the expansible work arbor E for supporting a plurality of gear blanks 30 On the work spindle comprises a hollow, cylindrical base member 31, an upper plate 32, and a lower plate 33 with a plurality of expansible split rings 34 stacked between the plates to form a cylinder of individually expansible elements. The lower plate 33 is supported on the top of base member 31. An expansible split ring 34 is provided for each blank to be positioned on the work arbor. Each expansible ring is engaged at spaced points on its inner periphery by a set of cam gears 36, eight in the illustrated embodiment, which are mounted on shafts 37, 38 parallel to the axis of the arbor and supported between plates 32 and 33 within the rings 34. The outermost points 39 of each set of cam gears define a circle of variable diameter concentric with the expansible ring greases and transverse to the arbor axis. Alternate shafts 37 extend through and beyond the upper plate and the'remaining shafts 38 are bolted between and space the plates 32 and 33. One of the shafts 38 is provided with a key 40 and each of the cam gears 36-mounted thereon has an arcuate slot-41 therein to allow-the cam gearslimited rotation on the shaft. All other shafts-and cam gears are constructed so the cam'gear. is capable of free'rotation about its shaft. The cam gears on each shaft 37, 38 are separated by spacers 42.

The cam surface 43 of the cam gear engages the inner periphery of the expansible ring and the gear portion 44 of the cam gear is in mesh with a gear 46 concentric with the expansible ring 34 and mounted on an arbor shaft 47 supported between plates 32 and 33 so as to be capable of limited rotation thereon. One gear 46is provided for driving each set of eightcam'gears, the cam gears being spaced about the circumference of the gear 46. The shaft 47'has a key 48 running lengthwise thereof, and each gear 46 is provided with an arcuate slot 49 to receive the key 48 and allow the gear limited rotation on the shaft. The arbor shaft lies along the axis of the arbor E, is journaled in the lower plate 33 by bearing 50, and has a reduced portion 51 extending below the lower plate for reasons as will hereinafter appear. The upper end of the arbor shaft 47 extends through an opening 52 in the upper plate 32 and is journaled in'the base of a pedestal type member 53 supported on the upper plate.

Each gear 46 on arbor shaft 47 is adapted to be rotated by friction disks 54 slidably keyed to the arbor shaft 47 by the key 48, there being a friction disk intermediate adjacent gears 46 and outwardly of each end gear. Since the gears and friction disks are free to move axially of the shaft, they are biased into engagement with each other by springs 55 supported between the top friction disk and a spring retainer plate 56 threaded on the upper end of arbor shaft '47.

It is now apparent that the workholder basically comprises a plurality of stacked expansible rings coaxial with the arbor shaft, each one being expanded, by a torque driven cam means comprising a plurality of cam gears. adapted to engage the inner periphery of the. expansible ring, the cam gears being circumferentially spaced about ,a driving gear mounted on the arbor shaft for limited rotation thereon, which driving gear is concentric with the expansible ring and driven by friction disks intermediate adjacent'driving gears. Upon rotation ofthe arbor shaft 47, the friction disks will drive the gears 46, thereby rotating the cam gears 36 and causing the outermost points 39 of the. cam gears to vary along a radius of the expansible split ring 34 engaged by the particular set of cam gears. Starting from the arbors contracted position, the cam gears will cause the ringsto expand until they engage the inner periphery of the gear, blank. When the gear blank is properly positioned the gear. 46 will be held against rotationand the friction disk will slip permitting further adjustment ofother blanks through their individual centering means. When all blanks have been centered the arbor shaft 47 may continue rotating until the.key 48 engages the .end of slot 49 in one ofthe gears 46 preventing further rotation of the arbor shaft with respect to,

the gears 46.

The pedestal member 53 has a circular base 57and a hollow cylindrical portion 58projecting upwardly therefrom coaxial with the arbor E. The circular base 57 acts as a guide for an annular clamp plate 59 movably mounted on shafts 37' aboyethe upper plate 32. The cylindrical portion 58 is provided'with an internal annular abutment 60 intermediate its ends.

The. gear blanks. to behobbed'are stacked .on thelower plate 33 beingsnpported by an adjustable annulanwear has a depending removable skirt 62, the lower edge of which engages the top gear blank. The skirt 62 is provided with spaced lugs 63 which cooperate with openings 64 in the upper plate 32 to detachably secure the skirt to the plate with a bayonet type of connection. The plate may be moved downwardly by applying downward pressure on a pilot 66 slidably mounted on the upper end of the cylindrical portion 58 of the pedestal member 53. The pilot has a projecting shoulder 67, the underside of which engages the ends of toggle arms 68 pivotally sup-. ported on shafts 37. Each toggle arm has an ear 69, which, when the arm is moved downwardly, engages a wear block 70 fixed to the upper side of the clamp plate 59. The pilot 66 is biased upwardly by a spring 71 interposed between the pilot and the internal abutment 60 within the pedestal member. A limiting rod 73 extends downwardly from the pilot member 66 through the cylindrical portion 58 and into an axial bore 75 in the upper end of shaft 47. The lower endof the rod is provided with a head 76 which is adapted to engage a knockout" plate 77 mounted between the end of arbor shaft 47 and the abutment 60 to limit the upward movement of the pilot. The knockout plate 77 is provided withan aperture to allow the passage of rod 73.

Preferably, the clamp plate 59 is biased towardsits releasing position. For this purpose springs 78, only one is shown, are interposed between the upper plate 32 and the clamp plate 59. The opposite ends of each spring are recessed in upper plate 32 and clamp plate 59 -re-' spectively.

A power mechanism is provided to. rotate the arbor shaft 47 to center the gear blanks 30 on the arbor E. The power mechanism comprises a drive shaft 80coaxial with the work spindle 12 and driven by a rotary air motor 81 detachably fixed to the lower end of the spindle. The drive shaft 80 extends through the work spindle, projects a short distance above the upper end of the spindle, and is supported by a bearing 83 in a transverse wall84 at the upper end of the spindle. The rotation of the drive shaft 80 rotates the arbor shaft 47 through planetary gearing H located within the base member 31. The upper end of the drive shaft 80 is provided with spur teeth 85 which mesh with a pinion gear 86 keyed to the lower end of a stub shaft 87 rotatively supported in a crank arm 88 on the reduced portion 51 of the arbor shaft 47. Keyed to the upper end of the stub shaft 87 is a planetary gear 89 which meshes withan internal-sun wheel 90 fixed to the base member 31. When the drive shaft 80 is rotated, the pinion 86 will walk around the drive shaft 80 causing the planetary gear 89=toalso walk around the sun wheel 90 thereby rotating the-arbor shaft 47 through the crank arm 88 and expanding the expansible rings 34 through the torque drive comprising the friction disks 54 and'the gears 46.

The air motor for rotating the drive shaft 80 is of conventional construction and is adapted'torotate on swivel joint 91 supported from the underside of the work head C by a vertical support 92 and horizontalsupports 93, 94'joined together by a block 95*." The horizontal supports 93, 94 are hollow and connecttosupply lines 96, 97 for supplying air to the distributor 98' of the air motor 81 through the swivel joint 91.

After all the gear blanks 39 have been centered on the arbor E, the key 48 in the arbor shaft will engage one end of the slot 49 in at least one of the gears 46 preventing additional rotation of the arbor shaft 47. This allowsair pressure to be continuously snppliedto the rotary motor during the hobbing operation. When the rotary motor has completed the centering operationthe gear blanks are clamped between the skirt 62 of theolanrp plate 5% and the annular wear ring.61 supported on the lower plate 33. The clamping pressure is exerted by the air cylinder F mounted in the core hole .16 ofthevertical column B. The cylindercomprises an inletconnection...

100 and a piston 19!; operated by-air pressure inv the cylin.-.

grsases der. A piston rod 102 extends downwardly from thepis ton 101 and is adjustably connected to the shank 103 of the tail center member 17. The shank 103 is slidingly supported in the tail 'slide 13 by a bushing 105. A cup-shaped member 106 is fixed to the lower end of the shank 103 and has a cap 107 rotatably supported therein by a roller bearing 108 and a bolt 109 which is threaded into the bottom of the cup-shaped member through the bottom of the cap. The cap 107 is free to rotate on the shank of the bolt 109. When the air pressure is applied to the air cylinder through inlet 100, the tail center member 17 is moved downwardly so that the cap 107 engages the pilot 66 moving the pilot downwardly against the action of spring 71 thereby causing the toggle arms 68 to move the clamp plate 59 downwardly to exert a clamping pressure through the skirt 62 on the blanks 30 stacked on the arbor E. The piston rod 102 and the shank 103 of the tail center member intermediate the tail slide and the air cylinder is enclosed in a telescoping guard 112. While the blanks 30 may be first centered and then the clamping pressure applied, it is desirable to apply a small clamping pressure during the centering operation.

Operation To position the gear blanks 30 on the arbor E, the skirt 62 is removed from the upper plate 32 and the gear blanks W are stacked on the wear ring 61. The skirt is then replaced on the arbor E and the arbor mounted on the spindle 12 so that the spur teeth 85 on the arbor drive shaft 80 mesh with the pinion 86 of the planetary drive.

Set screws 113 in the upper surface of the base member 31 are adapted to act against the lower end of shafts 37, 38 to enable the arbor shaft 47 to be aligned along the spindle axis. An air selector panel 115 is mounted on the vertical column B in a position accessible to the operator of the machine and controlsthe supply of air to the air motor 81 and the air cylinder F. The panel comprises an air control selector 116 and an unload button 117. When the air control selector is moved to its on position, the electrical circuit associated therewith is conditioned so that solenoid valves will operate to supply air to the air motor and air cylinder when a start button 118 located in the main control panel 119 is pushed inwardly to start the machine cycle. The electrical circuit is so arranged that a first solenoid valve is operated to supply air at a small pressure, preferably approximately 20 p. s. i. to the air cylinder F. This operates the piston to apply a clamping pressure to the pilot 66. After a predetermined time delay a second valve is operated to supply air to the rotary motor 81 to center the gear blanks on the arbor E. Another time delay follows the operation of the first and second solenoid valves after which full line pressure, preferably 80 p. s. i., is applied to the air cylinder E, thereby securely clamping the blanks 30 on the arbor E. After the machine has completed its cutting cycle, the gear blanks may be unclamped and the pressure of the rotary motor released by pushing the unload button 117 The centering mechaanism of the expansible arbor E is always returned to the same starting position by reason of the key 40 operating in the slot 41 of the respective cam gears on the particular shaft 38 in which the key is mounted. It is to be noted that air pressure may be supplied to the rotary motor 81 while the gear blanks are being hobbed. Slippage of the arbor shaft and the friction disks with respect to the gears 46 in such a case is prevented by reason of the key 48 in the arbor shaft 47 striking the end of slot 49 in at least one of the gears. If desired the blanks may be centered and clamped on the arbor E by manually controlling the valves for supplying air to the air cylinder and rotary motor. .To prevent the split rings 34 from being rotated during the centering operation, the rings are keyed to a post 120 supported between the upper plate 32 and lower plate 33 of the arbor E.

The control circuits for operating the respective motors of the machine and causing the machine to go through its hobbing cycle'are preferably similar to those disclosed in the aforesaid patent and will not be described in detail. Suffice it to say that after the gear blanks 30 have been properly positioned on the arbor E, the traverse motor is operated to move the work head C verticallly at a rapid traverse rate to bring the blank to cutting position with respect to the hob. At this point in the cycle, the traverse motor is automatically stopped and the cut motor started, thus continuing the movement of the work head but at a relatively slow feed rate. The feed movement continues until the blanks are cut, whereupon the cut motor is automatically stopped. After the work has been removed from the work head, the work head is returned to its original position by again depressing the start push button switch 118 to actuate the traverse motor in the opposite direction. The direction in which the cycle of operation is performed depends upon the setting of the selector controller switches 121, 122. The machine can be stopped at any time during its cycle of operations by depressing the stop push button switch 123. The length of travel of the rapid traverse approach movement, the feed movement, etc., is controlled by the adjustable stops 125, 126 and 127 carried by the work head C and adapted to actuate limit switches within the housing 128.

It will be seen-from the above that I have provided a new and improved hobbing machine having a novel means for quickly and easily securing a plurality of gear blanks in position to be hobbed, the work spindle of the machine including motor means for operating the means by which the gear blanks are centered and held in hobbing position.

While the preferred embodiment of the invention has been described with considerable detail the invention is not limited to the particular construction described and it is my intention to cover all adaptations, modifications and variations which come within the practice of those skilled in the art to which the invention relates and which fall within the scope of the appended claims.

Having thus described my invention, I claim:

1. An expansible work support for centering and holding a plurality of annular blanks about an axis of the work support comprising individual means defining an expansible ring for engaging each annular blank positioned on said support, and individual means for expanding the first said means including individual drive means operable with slippage upon the engagement of said means defining an expansible ring with an annular gear blank positioned on the support.

2. A work support for positioning and centering a plurality of annular blanks about an axis, each of said blanks being engaged and positioned by individual centering means comprising expansible means defining a ring for engaging the blank, individual means for expanding said expansible means into engagement with the blank including a friction drive, and a common shaft for operating the friction drives of each individual centering means.

3. A work support for centering and holding an annular blank about an axis, the blank being engaged and positioned by means comprising annular expansible means defining a ring for engaging the blank when positioned on said support, and means for expanding the first said means comprising a cam gear, the cam surface of which engages the first said means, and a friction drive for rotating said cam gear.

4. A work arbor for supporting a plurality of stacked annular blanks comprising an annular member expansible into substantially continuous engagement with the inner periphery of an annular blank stacked on the arbor, a plurality of cams circumferentially spaced along a circle within said member and rotatable to engage the inner periphery of said member and expand said member, and a torque drive for rotating said cams to expand said membet, said drive being operable with slippage upon engagement of said member with a blank positioned on the arbor.

5. In a work arbor for supporting and centering a plu rality of stacked gear blanks, individuial centering and supporting means for each gear blank comprising expansible annular means engageable with the inner periphery of the blank for centering the blank about and transverse to the axis of said arbor, means having a plurality of outermost points engaging said annular means and defining a circle lying in a plane transverse to the axis ofsaid arbor and having its center on said axis, means for varying the position of each of said points along a radius of said annular means to vary the circumference of the circle defined by said points.

6. In a work support for centering and holding an annular member, the combination of an expansible split ring for engaging said member, a plurality of rotatable cams circumferentially spaced along a circle concentric with said ring, the outermost points of said cams engaging said ring and defining a circle, the rotation of said cams moving the outermost point of each cam along a radius of said ring to vary the circumference of the circle defined by said outermost points, and means for rotating said cams.

7. A work support as in claim 6 wherein the means for rotating said cam comprises a driven member and a friction driving member.

8. In a work support for centering and holding an annular member, the combination of expansible annular means engaging said member, a plurality of rotatable cams circumferentially spaced about a circle concentric with said annular means, the outermost points of said cams engaging said annular means and defining a circle, the rotation of said cams moving the outermost point of each cam along a radius of said annular means to vary the circumference of the circle defined by said outermost points, means for rotating said cams, and a movable member adapted to apply a clamping pressure to the firstsaid member in a direction parallel to the axis of the support.

9. A work support as in claim 8 wherein said means for rotating said cam comprises a driven member and a friction drivingmember whereby a torque drive is produced.

10. An expansible work arbor for centering and holding a plurality of annular blanks comprising a rotatable shaft, a plurality of gears mounted on said shaft and capable of limited rotation with respect thereto, friction drive means interposed between said gears and said shaft, a plurality of cam gear sets, each of said sets comprisinga plurality of cam gears spaced about and in mesh with one of the first mentioned gears, the outermost points of the cam surface of the cam gears defining a circle the diameter of which is varied by the rotation of the cam gears, and a plurality of expansible members, each of said members being engaged by one of said sets of cam' gears.

11. In an arbor for holding'and centering a plurality of gear blanks about an axis about which said arbor is to be rotated, individual means for centering and positioning each of said gear blanks comprising an annular expansible member adapted to engage the gear blank, a plurality. of cam gears circumferentially spaced within said annular member along the circumference of a circle which lies in a plane transverse to said-axis and which has its center on said axis, the cam surfaces of each cam gear engaging the inner periphery of said annular member at its outermost point, said cam gears being adapted to be rotated to vary the position .of'the "outermost point of the cam gear along a radius of the annular member thereby varying the diameter'of the circle defined by said points, a gear concentric with said circle in :mesh with:- said gear cams for rotating -said gears, and, a friction disk for driving said gear, and a shaft along the axis of said arbor for driving said disks.

12. In an'arbor for holding and centering a plurality of gear blanks about an axis about which said workholder is to be rotated, individual means for centering and positioning each of said gear blanks comprising an annular expansible member adapted to engage said gear blank, a plurality of cam gears circumferentially spaced Within said annular member along the circumference of a circle which lies in a plane transverse to said axis and which has its center on said axis, the cam surfaces of each cam gear engaging the inner periphery of said annular member at the outermost point of said surface, said cam gears being adapted to be rotated to vary the position of the outermost point of the cam gear along a radius of the annular member thereby varying the diameter of the circle defined by said points, a gear in mesh with said cam gears for rotating said cam gears and a friction disk for driving said gear, and means adapted to apply a clamping pressure to said blanks along a line parallel to said axis.

13. In a Work arbor for supporting and centering a plurality of stacked annular blanks, individual expansible means for engaging and centering each blank comprising a set of circularly spaced cam-like members, means for rotatably supporting said members with the outermost points of said members of each set defining a circle, and individual drive means for each set of members for simultaneously rotating the members of the set to vary the diameter of the circle defined thereby, each of said drive means being capable of slippage upon engagement of the expansible means driven thereby with a blank positioned on the arbor.

14. In a work'arbor for supporting and centering a i plurality of stacked annular blanks, individual expansible means for engaging and centering each blank comprising a set of circularly spaced cam-like members, means for rotatably supporting said members with the outermost points of said members of each set defining a circle, individual drive means for each set of members for simultaneously rotating the members of the set to vary the diameter of the circle defined thereby, each of said drive means being capable of slippage upon engagement of the expansible means driven thereby with a blank positioned on the arbor, and a common shaft for actuating each of said drive means.

15. In a work support for centering and holding an annular member, expansible means for centeringthe annular member comprising a plurality of rotatable cams circumferentially spaced about a circle, the outermost points of said cams being varied to vary the diameter of said circle upon rotation of the cams, andmeans for rotating said cams comprising a friction torque drive capable of slippage upon engagement of the expansible means with the annular member positioned on the work support.

16. In an expansible work arbor for centering and holding an annular blank about an axis, a rotatable shaft, a gear mounted on said shaft and capable of rotation with respect thereto, friction drive means interposed between said gear and said shaft, a cam set comprising a plurality of spaced cams with the outermost points of the cams defining a circle concentric with said shaft, the diameter of said circle'being varied by the rotation of said cams, and means operatively connecting said cams to said gear for rotation thereby. 7

17. An expansible work arbor for centering and holding an annular blank comprising a rotatable shaft, a gear mounted on said shaft and capable of limited rotation with respect thereto, frictiondrive means interthe cam gears defining a circle having a diameter which is variable by the rotation of the cam gears.

18. In an arbor for holding and centering an annular blank about an axis about which the arbor is to be rotated, means for centering and positioning a blank on the arbor comprising expansible means defining a ring adapted to engage the annular blank, a plurality of carns circumferentially spaced within said means along the circumference of a circle which lies in a plane transverse to said axis and which has its center on said axis, the outermost points of said cams engaging said means and said cams being adapted to be rotated to vary the diameter of the circle defined by the outermost points thereof, a gear operatively connected to said cams for rotat- 10 ing said cams, a friction disk for driving said gear, and a shaft along the axis of said arbor for rotatably support ing said gears and driving said disk.

References Cited in the file of this patent UNITED STATES PATENTS 1,433,252 Barber Oct. 24, 1922 1,654,737 Kistner Jan. 3, 1928 1,772,203 Bush Aug. 5, 1930 1,919,239 McFall July 25, 1933 2,362,318 Staples I Nov. 7, 1944 2,499,781 Rothenberger Mar. 7, 1950 2,573,928 Peter Nov. 6, 1951 

